VALINE: CHARACTERISTICS, FUNCTIONS, RICH FOODS, BENEFITS - BIOLOGY - 2025

The valine belongs to the 22 amino acids identified as the "basic" components of proteins; it is identified with the acronym "Val" and with the letter "V". This amino acid cannot be synthesized by the human body, therefore, it is classified in the group of the nine essential amino acids for humans.

Many globular proteins have an interior rich in valine and leucine residues, since both are associated by hydrophobic interactions and are essential for the folding of the structure and the three-dimensional conformation of proteins.

Chemical structure of the amino acid Valine (Source: Clavecin via Wikimedia Commons)

Valine was purified for the first time in 1856 by V. Grup-Besanez from an aqueous extract of the pancreas. However, the name "valine" was coined by E. Fisher in 1906, when he managed to synthesize it artificially and observed that its structure was very similar to that of valeric acid, found in plants commonly known as "valerian".

Valine is one of the amino acids found in conserved positions in certain proteins shared by vertebrates, for example, at position 80 of vertebrate cytochrome C, leucine, valine, isoleucine and methionine are found in the same order.

Large amounts of valine are found in tissues or biomaterials with resistant, hard and elastic characteristics such as ligaments, tendons, blood vessels, threads or cobwebs, which provides flexibility and resistance thanks to its hydrophobic interactions with other amino acids.

A substitution of a glutamate residue for a valine residue in the β chain of hemoglobin, the protein responsible for transporting oxygen through the blood, causes a poor formation in the protein structure, which gives rise to hemoglobin "S".

This mutation causes sickle cell anemia or sickle cell disease, a pathological condition in which the red blood cells acquire a characteristic crescent or sickle shape, which differentiates them from normal blood cells, with a rounded and flattened appearance.

Some of the herbicides most used today have sulfonylurea and methyl sulfometuron as active compounds, which cause damage to the enzyme acetolactate synthase, necessary for the first step of synthesis of valine, leucine and isoleucine. The damage caused by these pesticides prevents grasses and weeds from developing normally.

characteristics

Valine is an amino acid with a five-carbon skeleton and belongs to the group of amino acids with aliphatic side chains. Its hydrophobic character is such that it can be compared to that of phenylalanine, leucine and isoleucine.

Amino acids that possess hydrocarbon chains in their R groups or side chains are commonly known in the literature as branched or branched chain amino acids. Valine, phenylalanine, leucine, and isoleucine are in this group.

Generally, the amino acids of this group are used as internal structural elements in protein synthesis, since they can associate with each other through hydrophobic interactions, "fleeing" from water and establishing the structural folds characteristic of many proteins.

Its molecular weight is around 117 g / mol and, since its R group or side chain is a branched hydrocarbon, it has no charge and its relative abundance in protein structures is little more than 6%.

Structure

Valine shares the general structure and the three typical chemical groups of all amino acids: the carboxyl group (COOH), the amino group (NH2), and a hydrogen atom (-H). In its R group or side chain it has three carbon atoms that give it very hydrophobic characteristics.

As is true for all chemical compounds classified as “amino acids”, valine has a central carbon atom that is chiral and is known as α-carbon, to which the four mentioned chemical groups are attached.

The IUPAC name for valine is 2-3-amino-3-butanoic acid, but some chemists also call it α-amino valerian acid and its chemical formula is C5H11NO2.

All amino acids can be found in the D or L form and valine is no exception. However, the L-valine form is much more abundant than the D-valine form and, in addition, it is more spectroscopically active than the D form.

L-valine is the form that is used for the formation of cellular proteins and is therefore, of the two, the biologically active form. It fulfills functions as a nutraceutical, a micronutrient for plants, a metabolite for humans, algae, yeasts and bacteria, among many other functions.

Features

Valine, despite being one of the nine essential amino acids, does not play a significant role in addition to its participation in protein synthesis and as a metabolite in its own degradation pathway.

However, bulky amino acids such as valine and tyrosine are responsible for the flexibility of fibroin, the main protein component of the silk threads produced by worms of the Bombyx mori species, commonly known as silkworms or silkworms. mulberry tree.

Tissues such as ligaments and arterial blood vessels are made up of a fibrous protein known as elastin. This is composed of polypeptide chains with repeated sequences of the amino acids glycine, alanine and valine, with valine being the most important residue with respect to the extension and flexibility of the protein.

Valine participates in the main synthesis routes of the compounds responsible for the characteristic smell of fruits. Valine molecules are transformed into branched and methylated derivatives of esters and alcohols.

In the food industry

There are many chemical additives that use valine in combination with glucose to obtain palatable odors in certain culinary preparations.

At a temperature of 100 ° C, these additives have a characteristic rye odor and at over 170 ° C they smell like hot chocolate, making them popular in food production in the baking and pastry industry.

These chemical additives use artificially synthesized L-valine, since their purification from biological sources is cumbersome and the required degree of purity is not usually obtained.

Biosynthesis

All the branched chain amino acids such as valine, leucine and isoleucine are mainly synthesized in plants and bacteria. Which means that animals such as humans and other mammals need to eat foods rich in these amino acids in order to meet their nutritional requirements.

Valine biosynthesis usually begins with the transfer of two carbon atoms from hydroxyethylthiamine pyrophosphate to pyruvate by the enzyme acetohydroxy isomeric acid reductase.

The two carbon atoms are derived from a second pyruvate molecule through a TPP-dependent reaction very similar to that catalyzed by the enzyme pyruvate decarboxylase, but which is catalyzed by dihydroxy acid dehydratase.

The enzyme valine aminotransferase, finally, incorporates an amino group to the ketoacid compound resulting from the previous decarboxylation, thereby forming L-valine. The amino acids leucine, isoleucine, and valine have great structural similarity, and this is because they share many intermediates and enzymes in their biosynthetic pathways.

The ketoacid produced during the biosynthesis of L-valine regulates some enzymatic steps by negative feedback or allosteric regulation in the biosynthetic pathway of leucine and the other related amino acids.

This means that biosynthetic pathways are inhibited by a metabolite generated in them that, when accumulated, gives cells a specific signal that indicates that a certain amino acid is in excess and therefore its synthesis can be stopped.

Degradation

The first three degradation steps of valine are shared in the degradation path of all branched chain amino acids.

Valine can enter the citric acid cycle or Krebs cycle to be transformed into succinyl-CoA. The degradation pathway consists of an initial transamination, catalyzed by an enzyme known as branched-chain amino acid aminotransferase (BCAT).

This enzyme catalyzes a reversible transamination that converts branched-chain amino acids into their corresponding branched-chain α-keto acids.

In this reaction, the participation of the glutamate / 2-ketoglutarate pair is essential, since the 2-ketoglutarate receives the amino group that is removed from the amino acid that is being metabolized and becomes glutamate.

This first reaction step of valine catabolism produces 2-ketoisovalerate and is accompanied by the conversion of pyridoxal 5'-phosphate (PLP) to pyridoxamine 5'-phosphate (PMP).

Next, 2-ketoisovalerate is used as a substrate for a mitochondrial enzyme complex, known as branched-chain α-ketoacid dehydrogenase, which adds a CoASH portion and forms isobutyryl-CoA, which is subsequently dehydrogenated and converted to methacrylyl-CoA.

Methacrylyl-CoA is processed downstream in 5 additional enzymatic steps involving hydration, removal of the CoASH portion, oxidation, addition of another CoASH portion, and molecular rearrangement, ending with the production of succinyl-CoA, which immediately enters the cycle of Krebs.

Valine rich foods

The proteins contained in sesame or sesame seeds are rich in valine, with almost 60 mg of the amino acid for each gram of protein. For this reason, sesame cookies, cakes and bars or nougat are recommended for children with diets deficient in this amino acid.

Soybeans, in general, are rich in all essential amino acids, including valine. However, they are poor in methionine and cysteine. Soy protein or texturing has very complex quaternary structures, but they are easy to dissolve and separate into smaller subunits in the presence of gastric juices.

Casein, which is typically found in milk and its derivatives, is rich in repeated sequences of valine. Like soy protein, this protein is easily broken down and absorbed in the intestinal tract of mammals.

It has been estimated that for every 100 grams of soy protein, about 4.9 grams of valine are ingested; while for every 100 ml of milk about 4.6 ml of valine are ingested.

Other foods rich in this amino acid are beef, fish, and various types of vegetables and greens.

Benefits of its intake

Valine, like a large part of amino acids, is a glucogenic amino acid, that is, it can be incorporated into the gluconeogenic pathway, and many neurologists claim that its intake helps maintain mental health, muscle coordination and reduce stress.

Many athletes consume tablets rich in valine, as they help regenerate tissues, especially muscle tissues. Being an amino acid capable of being incorporated into gluconeogenesis, it helps in the production of energy, which is not only important for physical activity but also for nervous function.

Foods rich in valine help maintain the balance of nitrogen compounds in the body. This balance is essential for the generation of energy from the ingested proteins, for the growth of the body and the healing.

Its consumption prevents damage to the liver and gallbladder, as well as contributes to the optimization of many bodily functions.

One of the most popular dietary supplements among athletes for increasing muscle volume and muscle recovery is BCAAs.

This type of tablet consists of tablets with mixtures of different amino acids, which generally include branched chain amino acids such as L-valine, L-isoleucine and L-leucine; they are also rich in vitamin B12 and other vitamins.

Some experiments carried out with pigs have shown that the requirements of valine are much higher and limiting for mothers during the lactation stage, since this amino acid helps the secretion of milk and produces improvements in the growth rate of lactating neonates.

Deficiency disorders

The recommended daily intake of valine for infants is around 35 mg for every gram of protein consumed, while for adults the amount is slightly lower (around 13 mg).

The most common disease related to valine and other branched-chain amino acids is known as "maple syrup urine disease" or "Ketoaciduria."

This is an inherited condition caused by a defect in the genes that code for the dehydrogenase enzymes of the α-ketoacids derived from leucine, isoleucine and valine, which are necessary for their metabolism.

In this disease the body cannot assimilate any of these three amino acids when they are obtained from the diet, therefore, the derived ketoacids accumulate and are expelled in the urine (they can also be detected in the blood serum and in the cerebrospinal fluid).

On the other hand, a diet deficient in valine has been linked to neurological pathologies such as epilepsy. It can also cause weight loss, Huntington's disease, and can even lead to the development of certain types of cancer, since the tissue repair system and the synthesis of biomolecules are compromised.

References

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